Is a new threat to oaks coming to Marin?

In this article from the Marin Independent Journal, Davey's Nick Crawford tells readers about a new threat to California's live oak trees.

By PJ Bremier

Published: July 19, 2014

About nine months ago, Akif Eskalen got a phone call from a homeowner in Southern California, concerned about a mysterious canker dripping foam on his oak tree.

Eskalen, an extension plant pathologist at the University of California at Riverside, headed out to inspect it.

"We identified our native California beetle, the western oak bark beetle (P. pubipennis) and identified the pathogen, a fungus species named Geosmithia pallida," he says.

In the process, he also discovered a new threat to California's beloved coast live oaks called foamy bark canker disease.

"Bark beetle is known to attack stressed plants and since we have been in a drought for several years, plants are stressed."

"Nobody has reported that pathogen in California before and the question is, is it new to California or has it been around before but not noticed?"

So far, he has documented affected oaks in the coastal areas of Los Angeles, Orange, Riverside, Santa Barbara, Ventura and Monterey counties.

Can it reach Marin? "It's hard to predict," he says. "What we know is that this disease is new and the native beetle can move and live anywhere in California."

Nicholas Crawford, a board certified master arborist with Davey Tree Expert Co. is monitoring the disease through its Southern California and Bay Area offices.

"The best news is that there are no reports of it yet in Marin or the Bay Area but, as we have seen in the past, things like this start in Southern California and move along the coast," he says. "It's just a matter of time before someone brings a truckload of firewood with foamy canker bark disease up to Marin and boom, it gets introduced. Buy your firewood locally."

However, he notes, "we could have it now and just don't know it until someone calls an arborist and gets a positive id."

How it happens

The tiny brown female western oak bark beetle burrows through the bark, laying larvae and spreading the fungus. As the larvae develop, they fly to other trees and spread it further.